docker: use subdomain as default in docker

Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile:1
 
 # STAGE 1: building the executable
-FROM docker.io/golang:1.20.6-alpine3.18 as builder
+FROM docker.io/golang:1.20.7-alpine3.18 as builder
 WORKDIR /build
 
 COPY go.mod go.sum ./
@@ -15,5 +15,8 @@ RUN go build -ldflags="-w -s" -o /go-avahi-cname
 # STAGE 2: build the container to run
 FROM scratch
 COPY --from=builder /go-avahi-cname /go-avahi-cname
+
 EXPOSE 5353/udp
+
 ENTRYPOINT ["/go-avahi-cname"]
+CMD [ "subdomain" ]